6

UCC3958 -1/-2/-3/-4

Figure 6. SIngle Cell Lithium-Ion Battery Protector IC Application Diagram

UDG-97152

Controlled Charge/Discharge Mode

When the chip senses an over-voltage condition, it pre-

vents any additional charging, but allows discharge. This

is accomplished by activating a linear control loop which

controls the gate of the MOSFET based on the differen-

tial voltage across its drain to source terminals. The lin-

ear loop attempts to regulate the differential voltage

across the MOSFET to 100mV. When a light load is ap-

plied to the part, the loop adjusts the impedance of the

MOSFET to maintain 100mV across it. As the load in-

creases, the impedance of the MOSFET is decreased to

maintain the 100mV control. At heavy loads (still below

“over-current” limit level), the loop will not maintain regu-

lation and will drive the gate of the MOSFET to the bat-

tery voltage (not the charge-pump output voltage).

The

drop (and associated power loss) across the internal

MOSFET in this mode of operation is lower than the typi-

cal solution of two external back-to-back MOSFETs,

where the body diode is conducting.

0

100

200

300

400

500

600

700

2.00

2.10

2.20

2.30

2.40

CELL VOLTAGE (V)

0.2Amp

1.0Amp

2.0Amp

Figure 5. Typical MOSFET Voltate Drop During

Charge in UV vs. Cell Voltage.

APPLICATION INFORMATION (continued)